One of the most difficult weed situations to deal with on the farm or acreage is weedy vines growing in hedges or trees. Wild cucumber, burcucumber, and honeyvine milkweed are the most common culprits. (Note: Field and hedge bindweed, and dodder can also be problematic, but will not be discussed here.) These plants shade the foliage of the host plant, and interfere with their ability to photosynthesis. This is especially damaging to evergreen trees, which don’t tolerate shading well.
Weedy vines are most noticeable in late summer and fall after considerable growth has occurred.
Native to the United States, wild cucumber and burcucumber are annual vines, found in the same plant family as cucumber and muskmelon, although neither produces edible fruits. Both grow from seed each year, and can be found growing wild in prairie ravines, fence rows, creek and stream banks, and ditches.
Wild cucumber (Echinocystis lobata), also known as balsamapple or mockcucumber, can grow 15 to 25 feet long. It has smooth stems and alternately placed, star-shaped leaves, each with 5 to 7 pointed lobes. Greenish white flowers grow on short stems arising from the leaf axils. The twining vines are aided in climbing by forked tendrils. It has oval fruits, up to two inches long, that are covered with sharp spines.
Burcucumber (Sicyos angulatus) vines can grow up to 10 feet tall. The alternate leaves are broad with three to five pointed lobes. The stems are slightly fuzzy and develop clasping forked tendrils, similar to grapevines. Both wild cucumber and burcucumber produce separate male and female flowers. In burcucumber, the male flowers are greenish-white to pale yellow growing on short stems, the female flowers are found in round clusters at the ends of short stems. Green to yellow fruits are covered with prickly bristles, and 1⁄2 to 3⁄4 inches long.
Honeyvine milkweed (Cynanchum laeve or Ampelamus albidus) is a vining member of the milkweed family that can grow 6 feet or more long. It differs from wild cucumber and burcucumber, in that it is a perennial plant, growing back from the crown each year. Plants spread through underground rhizomes, and can regenerate if all the root system is not killed or removed.
Honeyvine milkweed has triangular, or elongated heart-shaped leaves located opposite each other on long, smooth stems. It may be confused with bindweeds or morningglories, but they have alternate leaves. Clusters of small white flowers are found in the leaf axils and develop into smooth, slender, elongated milkweed pods. When the pods mature and open, they release brown flattened seeds with silky white hairs.
Wild cucumber and burcucumber seeds will germinate throughout the summer especially after rain, which makes periodic scouting and removal crucial for control. Scout areas with a history of problems, and pull or hoe weeds as soon as they emerge. In large areas, mowing can be effective. Repeated mechanical removal will prevent plants from producing additional seed and reduce weed pressure over time.
Simazine (Princep 4L) is labeled for preemergent control in shelterbelts to kill weed seeds as they germinate. Do not apply more than 4 qt. Princep 4L per acre (4 lb. a.i./A) per calendar year. Do not apply more than twice per calendar year.
Post Emergent Control
Glyphosate (RoundUp) can be sprayed or painted on small plants under trees to kill seedlings; it has practically no soil residual and if used carefully according to label directions will not damage desirable plants. DO NOT use Tordon or any product containing Dicamba, which have a period of soil residual activity and can move deeper in the soil to be absorbed by trees roots.
If weedy vines escape notice early in spring and grow up into trees, cut larger plant stems near the ground before plants begin to flower. DO NOT spray herbicides on vines in trees or hedges.